This invention relates generally to gas turbine components, and more particularly to cooled turbine shrouds.
Components of a gas turbine engine, for example stationary shrouds or shroud segments and their supporting structures, are exposed to a heated stream of combustion gases. It is desirable to operate a gas turbine engine at high temperatures most efficient for generating and extracting energy from these gases. However, such elevated temperatures frequently exceed the temperature capability of the basic component materials and can result in compromise of mechanical and/or physical properties, or distortion of the components. Consequently, use has been made of various heat-resistant coatings and/or cooling processes. If cooling is used, is it usually implemented by channeling relatively cooler air, for example from various points in the high-pressure compressor of the engine, and discharging it within or from a component to provide convection, impingement, or film cooling.
In some turbine configurations, a “bow wave” flow structure created by flow over a nozzle structure causes localized “hot spots” on an upstream shroud. Because the extraction of cooling flow reduces engine performance, it is known to apply film cooling selectively to those local hot spots only.
However, in certain situations this preferential cooling method is not effective. In some turbine configurations, the difference in part count between a row of shroud segments and the downstream nozzle segments staggers the location of the “bow wave” adjacent each shroud, making localized cooling of the shroud ineffective. This situation would instead require a row of film cooling holes distributed over the entire shroud segment to yield the same shroud durability protection. This would demand more cooling flow, and thus reduce engine performance. Furthermore, some shrouds incorporate a Thermal Barrier Coating (TBC) on their flowpath surfaces. The drilling of a cooling hole in this surface may ruin the TBC integrity.
Accordingly, there is a need for a turbine shroud which is efficiently cooled without the use of cooling holes therein.